Power conversion apparatus for electric vehicle

ABSTRACT

The object is to effectively reduce the resonant current flowing inside a converter unit and an inverter unit in a power conversion apparatus for an electric vehicle. The power conversion apparatus includes a converter unit that converts an alternating-current power into a direct-current power, an inverter unit that converts the direct-current power into an intended alternating-current power and supplies the intended alternating-current power to an electric motor that drives an electric vehicle, a housing that accommodates the converter unit and the inverter unit and a part of which is connected to ground, and a magnetic core that is disposed inside the housing and that suppresses the resonant current flowing between the converter unit and the inverter unit.

TECHNICAL FIELD

The present invention relates to a power conversion apparatus for anelectric vehicle.

BACKGROUND ART

Patent Literature 1 is an exemplary conventional literature thataddresses the issue of noise or the like in a power conversion apparatusfor an electric vehicle. According to Patent Literature 1, to suppress aleakage harmonic current flowing in a vehicle body via all pathwaysformed of a converter, an inverter, and a ground circuit, a filtercircuit is either disposed at each of the input side of the converter,the output side of the inverter, and the ground circuit or disposed ateither one of the input side of the converter and the output side of theinverter, and at the ground circuit.

-   Patent Literature 1: Japanese Patent Application Laid-open No.    H9-9412

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

In a power conversion apparatus for an electric vehicle, a converter, aninverter, and the like that constitute the power conversion apparatusneed to be installed under the floor of a vehicle body in a suspendedmanner. For this reason, in a conventional power conversion apparatusfor electric vehicle, a box shaped housing (hereinafter referred to as“housing”) is prepared to fix to the vehicle body, and is used toaccommodate main circuits of the converter and the inverter, connectionconductors (bus bars) that connect the converter and the inverter, andsmoothing capacitors that are connected between the connectionconductors. In addition, a cooler is installed outside of the housingfor cooling down heat generated from switching elements of the converterand the inverter.

In the case of an alternating-current electric vehicle, since thesecondary side of a transformer is decoupled from the ground, it isnecessary to fix the voltage to ground acting on each device to aconstant value and connect some point of the circuit at the secondaryside to ground. In that regard, in a power conversion apparatus forelectric vehicle configured in the abovementioned manner, it is commonpractice to connect the housing to ground.

Because of the abovementioned configuration in a conventional powerconversion apparatus for electric vehicle, the cooler that is placedclose to the switching elements and electrically-connected to thehousing happens to be the grounding point. The property of such a powerconversion apparatus is that there is an increase in stray capacitancebetween the direct-current bus bars of the converter and the inverter,and the housing or the cooler.

Conventionally, the problem of such stray capacitance has not beenunaddressed as a major issue. For example, upon reviewing variousconventional literatures including the abovementioned Patent Literature1, there is no discussion on the problems attributed to the straycapacitance of this kind.

Meanwhile, it was found by the inventors of the present invention that aresonant circuit is formed by the inductance component of a transformeror an electric motor that is connected to a power conversion apparatusfor electric vehicle and by the stray capacitance, and that the resonantcurrent flowing in the resonant circuit may act as the noise source thatoutputs unnecessary noise to the power supply side or the electric motorside.

Thus, as discussed above by the inventors of the present invention, ifthe converter and the inverter act as noise sources, then, depending onthe magnitude of the noise, there is a possibility that the noisecurrent flowing through an overhead contact line has an adverse effecton ground signal equipments, and noise current flowing through a motorwiring has an adverse effect on vehicle signal equipments or groundsignal equipments. In addition, in light of the recent technologicaltrend in which an increase in the motor output is considered inevitable,it is desirable to take some measures against the resonance phenomenonattributed to the stray capacitance of this kind.

The present invention has been made to solve the above problems in theconventional technology and it is an object of the present invention toprovide a technology that, with respect to a power conversion apparatusfor electric vehicle in which a converter and an inverter areaccommodated in a housing, enables effective reduction of the resonantcurrent attributed to the stray capacitance between the direct-currentbus bars of the converter and the inverter, and the housing.

Means for Solving Problem

In order to solve the abovementioned problem and achieve the object,power conversion apparatus for an electric vehicle according to thepresent invention includes a converter unit that converts analternating-current power into a direct-current power; an inverter unitthat converts the direct-current power into an intendedalternating-current power and supplies the intended alternating-currentpower to an electric motor that drives an electric vehicle; a housingthat accommodates the converter unit and the inverter unit and a part ofwhich is connected to ground; and an impedance element that is disposedinside the housing and that has an inductance component for suppressinga resonant current flowing between the converter unit and the inverterunit.

Effect of the Invention

According to a power conversion apparatus for an electric vehicle of thepresent invention, inside a housing that accommodates a converter unitand an inverter unit and that is partially connected to ground isdisposed a magnetic core that suppresses the resonant current flowingbetween the converter unit and the inverter unit. Because of that, itbecomes possible to effectively reduce the resonant current that isattributed to the stray capacitance between direct-current bus bars ofthe converter and the inverter, and the housing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a simplified circuit diagram of an exemplary configuration ofa power conversion apparatus for an electric vehicle according to apreferred embodiment of the present invention.

FIG. 2 is a schematic diagram of an exemplary installed state when thepower conversion apparatus for electric vehicle illustrated in FIG. 1 isinstalled with respect to a vehicle body.

FIG. 3 is a schematic diagram of a pathway of the resonant current thatis generated due to the stray capacitance between each connectionconductor and the housing of the power conversion apparatus and that isillustrated on a circuit diagram corresponding to FIG. 1.

FIG. 4 is a schematic diagram for explaining another embodiment ofarrangement of magnetic cores that is different from the arrangementillustrated in FIG. 1.

EXPLANATIONS OF LETTERS OR NUMERALS

-   1 overhead contact line-   2 current collecting device-   3 wheel-   4 rail-   6 transformer-   9 vehicle body-   11 electric equipment-   20 converter unit-   22 converter main circuit-   24P, 24N, 64P, 64N smoothing capacitor-   30 converter cooler-   32 fin base (converter unit)-   34 fin (converter unit)-   50 inverter cooler-   52 fin base (inverter unit)-   54 fin (inverter unit)-   60 inverter unit-   62 inverter main circuit-   70, 70 a to 70 d magnetic core-   80 housing-   82-84, 86-88 stray capacitance-   90 electric motor-   91 to 93 resonant current-   100 power conversion apparatus-   P, C, N connection conductor-   W running wind

BEST MODE(S) FOR CARRYING OUT THE INVENTION

A preferred embodiment for a power conversion apparatus for electricvehicle according to the present invention will be described below indetail with reference to the accompanying drawings. The presentinvention is not limited to the embodiment described below.

FIG. 1 is a simplified circuit diagram of an exemplary configuration ofa power conversion apparatus for an electric vehicle according to apreferred embodiment of the present invention. In FIG. 1, a powerconversion apparatus 100 includes a converter unit 20, an inverter unit60, and a magnetic core 70 that is inserted between the converter unit20 and the inverter unit 60. Each of those constituent elements isattached to a housing 80. To the input terminal of the power conversionapparatus 100 is connected a transformer 6. To the inverter unit 60,which is placed at the output terminal of the power conversion apparatus100, is connected an electric motor 90 that drives the electric vehicle.As the electric motor 90, it is suitable to use an induction motor or asynchronous motor.

Moreover, in FIG. 1, one end of the primary winding of the transformer 6is connected to an overhead contact line 1 via a current collectingdevice 2, while the other end thereof is connected to a rail 4, which isat the ground potential, via a wheel 3. The electric power (generally,alternating current of 20 KV to 25 KV) supplied from the overheadcontact line 1 is input to the primary winding of the transformer 6 viathe current collecting device 2, while the alternating-current powergenerated in the secondary winding of the transformer 6 is input to theconverter unit 20.

The converter unit 20 includes a converter main circuit 22 to whichswitching elements are bridge-connected and a converter cooler 30 forcooling down the bridge-connected switching elements. From the threeoutput terminals of the converter main circuit 22 are drawn connectionconductors P, C, and N that are connected to the inverter unit 60described later. The converter main circuit 22 performs PWM control oneach bridge-connected switching element to convert thealternating-current voltage supplied from the overhead contact line 1into an intended direct-current voltage and outputs the direct-currentvoltage. As the switching elements constituting the converter maincircuit 22, it is suitable to use, for example, IGBT elements embeddedwith anti-parallel diodes. Meanwhile, there are a number of knownexamples of the detailed configuration and the control method of theconverter main circuit 22, the description of which is omitted herein.In the example illustrated in FIG. 1, the converter main circuit 22 isillustrated as a three-level converter. Alternatively, the convertermain circuit 22 can also be configured from, for example, a two-levelconverter (known) and such a configuration also falls within the scopeof the present invention.

At the output terminals of the converter main circuit 22 are disposedsmoothing capacitors 24P and 24N that act as direct-current powersources for the inverter unit 60. More particularly, the smoothingcapacitor 24P is connected between the connection conductors P and C,while the smoothing capacitor 24N is connected between the connectionconductors C and N.

The inverter unit 60 includes an inverter main circuit 62 to whichswitching elements are bridge-connected and an inverter cooler 50 forcooling down the bridge-connected switching elements. To the three inputterminals of the inverter main circuit 62 are connected the connectionconductors P, C, and N as described above. Smoothing capacitors 64P and64N, which act as direct-current power sources, are respectivelyconnected between the connection conductors P and C and between theconnection conductors C and N. To the output terminals of the invertermain circuit 62 is connected the electric motor 90. The inverter maincircuit 62 performs PWM control on each bridge-connected switchingelement to convert the direct-current voltage input thereto into anintended alternating-current voltage and outputs the alternating-currentvoltage. As the switching elements constituting the inverter maincircuit 62, it is suitable to use, for example, IGBT elements embeddedwith anti-parallel diodes. Meanwhile, there are a number of knownexamples of the detailed configuration and the control method of theinverter main circuit 62, the description of which is omitted herein. Inthe example illustrated in FIG. 1, the inverter main circuit 62 isillustrated as a three-level inverter. Alternatively, the inverter maincircuit 62 can also be configured from, for example, a two-levelinverter (known) and such a configuration also falls within the scope ofthe present invention.

FIG. 2 is a schematic diagram of an exemplary installed state when thepower conversion apparatus illustrated in FIG. 1 is installed withrespect to a vehicle body. As illustrated in FIG. 2, the powerconversion apparatus 100 is disposed, along with another electricequipment 11, under the floor of a vehicle body 9. In the powerconversion apparatus 100, the converter unit 20, the inverter unit 60,and the magnetic core 70 and the like are accommodated in the housing80.

The converter cooler 30 includes a fin base 32 and a fin 34, and isdisposed at the bottom side of the converter unit 20 in such a way thatthe fin 34 comes into contact with the outside air. In an identicalmanner, the inverter cooler 50 includes a fin base 52 and a fin 54, andis disposed at the bottom side of the inverter unit 60 in such a waythat the fin 54 comes into contact with the outside air. By disposingthe power conversion apparatus 100 in the abovementioned manner, therunning wind W that is generated due to the running of the correspondingelectric vehicle and that flows in the opposite direction to the runningdirection flows to the fins 34 and 54, and the heat generated from theswitching elements is released into the atmosphere via the fins 34 and54.

In the abovementioned example, the converter cooler 30 and the invertercooler 50 are disposed outside the housing 80 in such a way that thefins thereof come into contact with the outside air. However, thearrangement is not limited to that example. For example, it is alsopossible to dispose each cooler inside the housing 80 to avoid damage tothe fins. In such an arrangement, that portion of each cooler disposedinside the housing 80 which comes into contact with the running wind Wcan be covered with, for example, a mesh-like structure. That enablesachieving a natural air cooling system as illustrated in FIG. 2 for thecoolers. Meanwhile, in the case of employing a forced air cooling systemwith an air blower or employing a water cooling system, the converterunit 20 and the inverter unit 60 can be accommodated in the housing 80without having to use a mesh-like structure or the like.

FIG. 3 is a schematic diagram of a pathway of the resonant current thatis generated due to the stray capacitance between each connectionconductor and the housing of the power conversion apparatus and that isillustrated on a circuit diagram corresponding to FIG. 1. As describedin the section of “PROBLEM TO BE SOLVED BY THE INVENTION”, the resonantcurrent is a current that flows to the side of the transformer 6 or theelectric motor 90 by the stray capacitance formed between thedirect-current bus bars of the converter unit 20 and the inverter unit60, and the housing 80 and by the inductance component of thetransformer 6 or the electric motor 90 connected to the power conversionapparatus 100.

In the converter unit 20 illustrated in FIG. 3, stray capacitances 82 to84 are formed as illustrated between the direct-current bus barsincluding the connection conductors P, C, and N, respectively, and thehousing 80. In the inverter unit 60, stray capacitances 86 to 88 areformed as illustrated between the direct-current bus bars including theconnection conductors P, C, and N, respectively, and the housing 80.Each stray capacitance is illustrated by integrating stray capacitancecomponents that are generated in each part of the converter main circuit22 and the inverter main circuit 62.

When such stray capacitance components are present, resonance (seriesresonance) occurs between the inductance components of the transformer 6and the electric motor 90, and the stray capacitance components. Thus,the impedance for a particular frequency band (e.g., 1 to 2 MHz band)decreases and the current of only that particular frequency band getsamplified. As a result, in the housing 80, a resonant current 91 flowsvia the stray capacitances 82 and 86, a resonant current 92 flows viathe stray capacitances 83 and 87, and a resonant current 93 flows viathe stray capacitances 84 and 88.

Therefore, in the present embodiment, the magnetic core 70 having anintended inductance component is so disposed that the connectionconductors P, C, and N that connect the converter unit 20 and theinverter unit 60 are passed through the magnetic core 70. By disposingthe magnetic core 70, it becomes possible to shift the frequency for themaximum resonant current (hereinafter referred to as “resonantfrequency”) to a frequency band that does not affect, for example,vehicle signal equipments, ground signal equipments, or the like.Moreover, by inserting the magnetic core 70, it becomes possible toraise the inductance of that frequency band in which resonance is anissue. As a result, the resonant current in that particular frequencyband can be reduced and the magnitude of the noise attributed to theresonant current can be reduced to a level that does not cause anyproblem.

Meanwhile, as the material for the magnetic core 70, it is possible touse, for example, a ferrite material or an amorphous material. Sincesuch a material has the property of low impedance at a low frequencyband, there is practically no effect on power transmission in the powersupply frequency band.

Moreover, the size of the magnetic core 70 (length of the outercircumference, length of the inner circumference, thickness, aspectratio or the like) can be suitably determined according to the capacityof the converter unit 20 and the inverter unit 60, or the size andarrangement of each connection conductor, or the like. Furthermore, theinductance value of the magnetic core 70 can be suitably selecteddepending on the magnitude of the resonant frequency and the straycapacitance.

The abovementioned stray capacitance components are mainly attributed tothe facts that the direct-current bus bars including the connectionconductors P, C, and N are placed close to the housing 80 and that thehousing 80 is connected to ground such that it is at the same electricpotential as the ground potential. Therefore, the stray capacitanceoccurs even if no cooler is disposed. Thus, the abovementionedcountermeasures are effective even for a configuration with no cooler.However, in comparison with a configuration with no cooler, aconfiguration with cooler has larger stray capacitance components due tothe effect of the area of a heat releasing fin. Thus, it is desirable toperform suitable selections for each type of configuration.

FIG. 4 is a schematic diagram for explaining another embodiment ofmagnetic cores that is different from the arrangement illustrated inFIG. 1. In the embodiment illustrated in FIG. 1, the magnetic core 70 isdisposed between the converter unit 20 and the inverter unit 60.Alternatively, the magnetic core 70 can also be disposed inside each ofthe converter unit 20 and the inverter unit 60. For example, inside theconverter unit 20, magnetic cores 70 a and 70 c can be disposed ateither of the output side (the side of the connection conductors) or theinput side (the side of the converter main circuit) with respect to thesmoothing capacitors 24P and 24N as illustrated in FIG. 4. Similarly,inside the inverter unit 60, magnetic cores 70 b and 70 d can bedisposed at either of the input side (the side of the connectionconductors) or the output side (the side of the inverter main circuit)with respect to the smoothing capacitors 64P and 64N as illustrated inFIG. 4. Even for such a configuration, the magnetic cores are disposedin the loop pathway through which the resonant current flows. Thus, itis possible to reduce the resonant current attributed to the straycapacitance and shift the resonant frequency to an intended frequencyband as the advantages of the present application.

Meanwhile, the magnetic core according to the present embodiment isdisposed with the aim of reducing the resonant current that flows due tothe resonant circuit formed inside the power conversion apparatus. Inaddition, since the potential fluctuation due to the resonant current issuppressed, the common-mode current flowing to the side of thetransformer or the side of the electric motor is also reduced.

As described above, in the power conversion apparatus for electricvehicle according to the present embodiment, inside a housing thataccommodates a converter unit and an inverter unit and that is partiallyconnected to ground is disposed a magnetic core for suppressing theresonant current flowing between the converter unit and the inverterunit. Therefore, it becomes possible to effectively reduce the resonantcurrent attributed to the stray capacitance between the direct-currentbus bars of the converter and the inverter, and the housing.

Moreover, in the present embodiment, the magnetic core is disposed as anelement for suppressing the resonant current that flows between theconverter unit and the inverter unit. Instead of the magnetic core, itis also possible to use a reactor or a common-mode choke coil as animpedance element having an inductance component. Thus, the essentialpoint is that, as long as the resonant frequency can be shifted to afrequency band that does not affect, for example, vehicle signalequipments, ground signal equipments, or the like, it is possible to usean impedance element of any type.

INDUSTRIAL APPLICABILITY

In this way, the present invention is suitable in effectively reducingthe resonant current that is generated due to the stray capacitancebetween direct-current bus bars of a converter and an inverter, and ahousing that accommodates the converter and the inverter in a powerconversion apparatus for electric vehicle.

1. A power conversion apparatus for an electric vehicle comprising: aconverter unit that converts an alternating-current power into adirect-current power; an inverter unit that converts the direct-currentpower into an intended alternating-current power and supplies theintended alternating-current power to an electric motor that drives anelectric vehicle; a housing that accommodates the converter unit and theinverter unit and a part of which is connected to ground; and animpedance element that is disposed inside the housing and that has aninductance component that suppresses a resonant current flowing betweenthe converter unit and the inverter unit, wherein the impedance elementis disposed at least at either one of in the converter unit at an outputside of a converter main circuit included in the converter unit and inthe inverter unit at an input side of an inverter main circuit includedin the inverter unit.
 2. The power conversion apparatus for an electricvehicle according to claim 1, wherein the impedance element is disposedbetween the converter unit and the inverter unit so that a connectionconductor that connects the converter unit and the inverter unit ispassed through the impedance element.
 3. The power conversion apparatusfor an electric vehicle according to claim 1, wherein the impedanceelement is a magnetic core.
 4. The power conversion apparatus for anelectric vehicle according to claim 2, wherein the impedance element isa magnetic core.
 5. A power conversion apparatus for an electric vehiclecomprising: a converter unit that converts an alternating-current powerinto a direct-current power, the converter unit including an outputterminal; an inverter unit that converts the direct-current power intoan intended alternating-current power and supplies the intendedalternating-current power to an electric motor that drives an electricvehicle, the inverter unit including an input terminal; a connectionconductor connected to the output terminal of the converter unit and theinput terminal of the inverter unit; and an impedance element that hasan inductance component that suppresses a resonant current flowingbetween the output terminal of the converter unit and the input terminalof the inverter unit, wherein the impedance element is adjacent to theconnection conductor and is disposed at least at either one of in theconverter unit at the output terminal of the converter unit and in theinverter unit at the input terminal in the inverter unit.